1. WCDMA Air Interface Training Part 5 WCDMA Acquisition, Synchronization, and Handover

2. WCDMA Physical Layer Procedures
Physical Layer Timing and procedures
BS Downlink timing
Fast Synchronization Codes
Synchronization Code 1 (PSC)
Synchronization Code 2 (SSCi)
Downlink Scrambling Codes
Used by UE to distinguish desired Base Station
8192 possible codes, 64 Scrambling Code Groups
Slot Synchronization
Frame Synchronization
System Timing Synchronization
Soft Handover
Random Access protocol
Packet Access protocol
Inter-Frequency Handover

3. Downlink Transmission Timing
3GPP TS ¶ 7.0
10 ms Frame
Primary SCH
SCH (PSC+SSC) P-CCPCH S-CCPCH PICH AICH PDSCH DPCH
Secondary SCH
Common Pilot Channel
CPICH (Common Pilot Channel)
P-CCPCH, (SFN modulo 2 = 0)
P-CCPCH, (SFN modulo 2 = 1)
Primary CCPCH (Broadcast Data)
t S-CCPCH,k
Secondary CCPCH (Paging, Signaling)
k:th S-CCPCH
t PICH
Paging Indication Channel
PICH for n:th S-CCPCH
t DPCH,n
Dedicated Physical Control/Data Channel
n:th DPCCH/DCDPH
Downlink Shared Channel
Any PDSCH
AICH access slots #0 #1 #2 #3
#14
#13
#12
#11
#10 #9 #8 #7 #6 #5 #4
t S-CCPCH,k = N x 256 chips
t DPCH,n = N x 256 chips
t PICH = 7680 chips (3 slots)

4. Downlink Scrambling Codes
3GPP TS ¶ 5.2.2
Downlink Scrambling Codes
Used to distinguish Base Station transmissions on Downlink
Each Cell is assigned one and only one Primary Scrambling Code
The Cell always uses the assigned Primary Scrambling Code for the Primary and Secondary CCPCH’s
Secondary Scrambling Codes may be used over part of a cell, or for other data channels
8192 Downlink Scrambling Codes Each code is 38,400 chips of a (262,143 chip) Gold Sequence
Code Group #1
Code Group #64
Primary SC0
Primary SC7
Primary SC504
Primary SC511
Secondary Scrambling Codes
(15)
Secondary Scrambling Codes
(15)
Secondary Scrambling Codes
(15)
Secondary Scrambling Codes
(15)

5. Downlink Scrambling Codes
3GPP TS ¶ 5.2.2
Downlink Scrambling Code Generation
10 mSec Gold Code formed by Modulo-2 Addition of 38,400 chips from two m-sequences
Primary Scrambling code i (where i = 0,...,511) is generated by offsetting the X sequence by (16*i) clock cycles from the Y sequence I Q 1 2 3 4 5 6 7 8 9 17 16 15 14 13 12 11 10 X Y
Initial Conditions:
x(0) =1; X(1)... X(17) = 0 y(0) ... Y(17) = 1

6. Synchronization Codes
3GPP TS ¶ 5.2.3
Synchronization Codes (PSC, SSC)
Broadcast by BS
First 256 chips of every SCH time slot
Allows UE to achieve fast synchronization in an asynchronous system
Primary Synchronization Code (PSC)
Fixed 256-chip sequence with base period of 16 chips
Provides fast positive indication of a WCDMA system
Allows fast asynchronous slot synchronization
Secondary Synchronization Codes (SSC)
A set of 16 codes, each 256 bits long
Codes are arranged into one of 64 unique permutations
Specific arrangement of SSC codes provide UE with frame timing, BS “code group”
P-CCPCH
(PSC + SSC + BCH)
256 Chips
2304 Chips
Broadcast Data (18 bits)
SSCi
PSC

7. Primary Synchronization Code
3GPP TS ¶ 5.2.3
Primary Synchronization Code (PSC)
let a = <1, 1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, -1, -1, 1>
PSC( ) = < a, a, a, -a, -a, a, -a, -a, a, a, a, -a, a, -a, a, a >
Note: PSC is transmitted “Clear” (Without scrambling)
SCH
BCH
256 Chips
2304 Chips
PSC
Broadcast Data (18 bits)
SSCi 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 Frame = 15 slots = 10 mSec

8. Secondary Synchronization Code Group
3GPP TS ¶ 5.2.3
16 Fixed 256-bit Codes; Codes arranged into one of 64 patterns
SSCi
SSC1
SSC15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 Frame = 15 slots = 10 mSec
Note:
The SSC patterns positively identify one and only one of the 64 Scrambling Code Groups.
This is possible because no cyclic shift of any SSC is equivalent to any cyclic shift of any other SSC.

9. 10 mSec Frame (15 slots x 666.666 uSec)
Slot Synchronization
3GPP TS Annex C
Slot Synchronization using Primary Synchronization Code
10 mSec Frame (15 slots x uSec)
BCH Data
PSC [1]
PSC [2]
PSC [3]
PSC [4]
PSC [15]
Matched Filter (Matched to PSC)
P-CCPCH
(PSC)
Matched Filter Output
time

10. Frame Synchronization, SCG ID
3GPP TS Annex C
Frame Synchronization using Secondary Synchronization Code
10 mSec Frame (15 slots x uSec)
SSC [1]
BCH Data
SSC [2]
BCH Data
SSC [3]
BCH Data
SSC [4]
BCH Data
SSC [15]
BCH Data
Matched Filter Matched to SSC code group pattern
SSC [1]
SSC [2]
SSC [3]
SSC [4]
SSC [5]
SSC [6]
SSC [7]
SSC [8]
SSC [9]
SSC [10]
SSC [11]
SSC [12]
SSC [13]
SSC [14]
SSC [15]
SSC Code Group Pattern provides
Frame Synchronization
Positive ID of Scrambling Code Group
Remember, no cyclic shift of any SSC is equal to any other SSC
Matched Filter Output
time

11. message part (UE Identification)
Random Access
3GPP TS ¶ 7.3
Random Access Attempt and AICH Indication
RACH
AICH
4096 chips (1.066 msec)
Pre-amble
RACH
message part (UE Identification)
Pre-amble
Pre-amble UE
No Ind.
No Ind.
Acq. Ind. BS

12. Random Access Procedure
3GPP TS ¶ 6.1
Prior to initiating a Random Access attempt, the UE receives:
The preamble spreading code for this cell
The available random access signatures
The available spreading factors for the message part
The message length (10 ms or 20 ms)
Initial preamble transmit power
Power ramping factor
The AICH transmission timing parameter
The power offset DPp-m between preamble and the message part.
Transport Format parameters

13. Random Access Preamble Signatures
3GPP TS ¶
Preamble codes are 16-long Orthogonal Walsh Codes.
Preamble = [ P0, P1, … P15 ] repeated 256 times (4096 chips total).
Preamble codes help the BS distinguish between UE making simultaneous Random Access Attempts.

14. Random Access Scrambling Codes
3GPP TS ¶ 4.3.3
Random Access Preamble Scrambling Codes
Preamble Scrambling Code is a 4096-chip segment of a 225-long Gold Code
The UE targets one BS by using the BS’s indicated preamble scrambling code
“All UE accessing this cell shall use Random Access Preamble Spreading Code n1 ”
“All UE accessing this cell shall use Random Access Preamble Spreading Code n2 ”

15. Acquisition Indication Channel
3GPP TS ¶
Acquisition Indication Channel (AICH)
Transmits Acquisition Indicators in response to UE Access Attempts
AI’s are derived from the UE’s Access Preamble Signature
Identifies the UE which is the target of the AICH response
AI part
1024 chips a0 a1 a2
a30
a31
(Transmission Off)
AS #14
AS #0
AS #1
AS #i
AS #14
AS #0
20 ms

16. RACH Message Slot (0.666 mSec)
Random Access Message
3GPP TS ¶ 5.2.2
Random Access Message
Sent only after positive AICH indication
RACH Data Slot (0.666 mSec) I
Random Access Message (10, 20, 40, or 80 bits per slot)
RACH Message Slot (0.666 mSec) Q
Pilot (8 bits)
TFCI (2 bits) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 Frame = 15 slots = 10 mSec

17. Random Access Offset Timing
3GPP TS ¶
Random Access Procedure
Available RACH time slots determined by upper layers, sent over BCH UE selects slot based on pseudo-random algorithm P
Message
= Random Access Transmission
radio frame: 10 ms
radio frame: 10 ms
5120 chips #0 #1 #2 #3 #4 #5 #6 #7 #8 #9
#10
#11
#12
#13
#14
Access slot #0
Random Access Transmission
Access slot #1
Random Access Transmission
Access slot #7
Random Access Transmission
Access slot #8
Random Access Transmission
Access slot #14

18. Acquisition and Synchronization
Physical Layer Procedures
1) UE Acquisition and Synchronization
P-CCPCH
(PSC + SSC + BCH)
Initiate Cell Synchronization
UE Monitors Primary SCH code, detects peak in matched filter output
Slot Synchronization Determined >
UE Monitors Secondary SCH code, detects SCG and frame start time offset
Frame Synchronization and Code Group Determined >
UE Determines Scrambling Code by correlating all possible codes in group
Scrambling Code Determined >
UE Monitors and decodes BCH data
BCH data, Super-frame synchronization determined >
UE adjusts transmit timing to match timing of BS Chips
Cell Synchronization Complete

19. Cell Synchronization Complete
Random Access
P-CCPCH
(PSC + SSC + BCH)
Physical Layer Procedures
2) UE Requests System Access and Registration
Cell Synchronization Complete
UE Reads Random Access parameters from BS; Calculates Random Access probe power
Initiate Random Access Attempt; Respond to Authentication challenge
When system Registration is complete, UE enters Idle mode

20. Establishing a Dedicated Channel
3GPP TS ¶ 4.3.2
Physical Layer Procedures
3) Establishing a Dedicated Channel
UE in Idle Mode
BS Begins transmission of downlink DPCCH/DPDCH
UE Establishes chip and frame sync to UTRAN
UE begins transmission of Reverse Link Channel, Responds to TPC bits from BS
UTRAN establishes Reverse Link chip and frame sync, Responds to TPC bits from UE
UE and BS notify upper layers that synchronization is complete
Dedicated Channel Established

21. Packet Channel Access AICH DPCCH
3GPP TS ¶ 7.4
AICH DPCCH
CCC (CPCH Control Commands) e.g., Start-of-Message , Emergency-Stop
CPCH DPCCH DPDCH
DL-DPCCH Slot (SF=256)
TPC
TFCI
CCC
Pilot
CSICH
AP-AICH
CD/CA-ICH
PCPH PC-Preamble Slot (SF=256)
DPCCH Slot (SF=256)
Pilot
TFCI
FBI
TPC
Pilot
TFCI
FBI
TPC
DPDCH (Data); SF 4 to 256 AP
CDP AP
PCPCH Uplink Data Packet ‘N’ x 10 msec Frames
Power Control Preamble (0 or 8 slots)

22. Packet Channel Access
3GPP TS ¶ 7.4
Prior to Packet Access, the UE receives from the UTRAN:
UL Access Preamble (AP) scrambling code.
UL Access Preamble signature set.
The Access preamble slot sub-channels group.
AP- AICH preamble Channelization code.
UL Collision Detection(CD) preamble scrambling code.
CD Preamble signature set.
CD preamble slot sub-channels group.
CD-AICH preamble Channelization code.
CPCH UL scrambling code.
DPCCH DL Channelization code.([512] chip).
CSICH/CA message indicating channel availability

23. CPCH Status Indication Channel
3GPP TS ¶
CPCH Status Indication Channel (CSICH)
Transmits Indicators to convey PCPH Channel Availability
1024 chips 8 bits/slot SF = 256
4096 chips
Higher layers provide mapping of status indicators to availability of CPCH resources
(Transmission Off) b0 b1 b2 b3 b4 b5 b6 b7
AS #14
AS #0
AS #1
AS #i
AS #14
AS #0
20 ms

24. Access Preamble Indication Channel
3GPP TS ¶
Access Preamble Indication Channel (AP-AICH)
Transmits Indicators in response to UE CPCH Access Attempt
API’s are derived from the UE’s CPCH Access Preamble Signature
Identifies the UE which is the target of the AP-AICH response
1024 chips a0 a1 a2
a30
a31
(Transmission Off)
AS #14
AS #0
AS #1
AS #i
AS #14
AS #0
20 ms

25. CD/CA Indication Channel
3GPP TS ¶
Collision Detection/Channel Assignment Indication Channel
Transmits Acquisition Indicators in response to UE CD preambles
CDI’s are derived from the UE’s CD Preamble Signature
Optionally may transmit CPCH Channel Assignment Indicators
1024 chips a0 a1 a2
a30
a31
(Transmission Off)
AS #14
AS #0
AS #1
AS #i
AS #14
AS #0
20 ms

26. WCDMA Soft Handover Each cell uses a different Scrambling Code
Each cell has an independent time reference
CPICH and System Frame timing between cells is arbitrary
Originating BS
SC5
Destination BS
SC6
SC1
SC7
SC8
SC4

27. The WCDMA Soft Handover Problem...
WCDMA Base Stations have Asynchronous timing references
IS-95/cdma2000 BS’s are synchronized to GPS!
0.666 msec DPCCH/DPDCH slot
Data 1
TPC
TFCI
Data 2
Pilot 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
10 msec DPCCH/DPDCH frame
BS 2
CPICH 2
CPICH 2
CPICH 2
CPICH 2
BS 1
10 msec frame
DPCCH/DPDCH
DPCCH/DPDCH
DPCCH/DPDCH
DPCCH/DPDCH
CPICH 1
CPICH 1
CPICH 1
CPICH 1
DPCCH/DPDCH
DPCCH/DPDCH
DPCCH/DPDCH
DPCCH/DPDCH
Toffset

28. WCDMA Handover Scenarios
3GPP TS
Core Network Iu Iu
RNS
RNS
Iur
RNC
RNC
UTRAN 
Iub
Iub
Iub
Iub
Node B
Node B
Node B
Node B
Inter-Node (Hard or Soft)
Inter-RNS (Soft with Iur; Hard with no Iur)
Intra-Node (Softer)

29. WCDMA Soft Handover
3GPP TS ¶ 9.0
To facilitate asynchronous handover, timing adjustments are made by the UE, the RNC, and the Core Network
Core Network
Vocoder
Time Alignment
UTRAN
RNC
RNS
RNC
RNS
Transport Channel Frame Alignment
Node B
Node B
Node B
Node B
Node B
Node B
Radio Synchronization UE

30. WCDMA Soft Handover Soft Handover Initiation DOCUMENTTYPE
TypeUnitOrDepartmentHere
TypeYourNameHere
TypeDateHere
WCDMA Soft Handover
Soft Handover Initiation
(1)
UTRAN informs UE of neighboring cell information
(2)
UE measures CPICH power and time delay from adjacent cells
(3)
UE Reports measurements to UTRAN
(4)
UTRAN decides the handover strategy
BS 2
CPICH 2
CPICH 2
CPICH 2
CPICH 2
BS 1
10 msec frame
CPICH 1
CPICH 1
CPICH 1
CPICH 1
DPCCH/DPDCH
DPCCH/DPDCH
DPCCH/DPDCH
DPCCH/DPDCH
UE Reports Toffset
to UTRAN
Toffset
UTRAN

31. WCDMA Soft Handover Soft Handover Execution (5)
UTRAN Commands BS2 to adjust DPCH timing by Toffset
(6)
UE Rake Receiver Synchronizes to BS2 DPCCH/DPDCH
(7)
UE in soft handover with BS1 and BS2 DPCCH/DPDCH’s
(8)
When BS2 sufficiently strong, drop BS1. (Handover complete)
BS 2
CPICH 2
BS 1
10 msec frame
DPCCH/DPDCH
CPICH 1
CPICH 1
CPICH 1
CPICH 1
Toffset
DPCCH/DPDCH
DPCCH/DPDCH
DPCCH/DPDCH
DPCCH/DPDCH
UE Reports Toffset
to UTRAN
Toffset
UTRAN Commands BS2
to adjust DPCH timing
by Toffset
UTRAN

32. Inter-Frequency Handover
To allow inter-frequency measurements, data is compressed in time so that some of the 10 mSec frame is available for measurements.
8 to 14 slots per frame may be used
Data compression can be accomplished by:
Decreasing the Spreading Factor by 2:1
Increases Data Rate so bits get through twice as fast!
Puncturing bits
weakens FEC coding
Higher layer scheduling
Reduces available timeslots for user traffic

33. Compressed Mode Operation
3GPP TS ¶ 4.4.3
1 to 7 slots per frame diverted for hard handover processes
The complete TFCI word must be transmitted every frame, even in Compressed Mode. Compressed Mode Slot formats (A,B) contain higher proportion of TFCI bits per slot compared with normal slots.
10 mSec Frames (15 slots)
Normal Operation 11 12 13 14 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 15 2 3 4 5 6
Compressed-Mode; single-frame method 11 12 13 14 15 1 2 3 4 5 11 12 13 14 15 1 2 3 4 5 6
Transmission Gap
Compressed-Mode; double-frame method 11 12 13 14 15 1 2 3 4 5 6 7 8 9 10 11 12 4 5 6
Transmission Gap

34. GSM 26-frame TCH multiframe (120 ms)
Handover to/from GSM
Handover to/from GSM
GSM handover is an explicit requirement in WCDMA
Facilitated by commonality of multi-frame structures
12 WCDMA 10 mSec Frames (120 ms) 1 2 3 4 5 6 7 8 9 10 11 12
GSM 26-frame TCH multiframe (120 ms) T T T T T T T T T T T S T T T T T T T T T T T T T I
T = Traffic Frame
S = SACCH Frame
I = Idle Frame